可樂定
可樂定是一種**中樞 alpha-2 腎上腺素受體激動劑**，在獸醫學中傳統上用作診斷犬隻生長激素 (GH) 缺乏症或嗜鉻細胞瘤的診斷劑。它也作為難治性**炎症性腸病 (IBD)**（特別是貓）的輔助治療，以及用於嚴重疼痛或手術麻醉的硬膜外輔助藥物。 > **臨床要點（藥理學補充）：** > * 雖然藥典強調其診斷和胃腸道用途，但可樂定在現代獸醫行為醫學中越來越多地被標示外使用，以控制犬隻的**恐懼性焦慮、噪音恐懼症和情境性恐慌**。 > * 它透過抑制交感神經喚醒來提供抗焦慮和鎮靜作用，通常不會出現其他鎮靜劑常見的嚴重共濟失調。 > * 由於其心血管效應，需要仔細篩選病患並調整劑量。
作用機制: Clonidine acts centrally at the **brain stem**, stimulating **alpha-2 adrenoreceptors**. * **Cardiovascular/Sympathetic:** Stimulation of presynaptic **alpha-2 receptors** (e.g., in the **locus coeruleus**) → decreases norepinephrine release → reduces sympathetic outflow from the CNS → decreased peripheral resistance, heart rate, and blood pressure. * **Endocrine:** Stimulates **GHRH (Growth Hormone Releasing Hormone)** → transient release of **Growth Hormone (GH)**. * **Analgesia:** Stimulates presynaptic and postjunctional **alpha-2 adrenoreceptors** in the dorsal horn of the spinal cord → blocks pain signal transmission to the brain. * **Gastrointestinal:** Alpha-2 stimulation alters enteric nervous system tone, increasing fluid absorption and decreasing motility, aiding in refractory IBD.
各物種劑量
- Adjunctive antidiarrheal therapy for refractory cases of inflammatory bowel disease · 5-10 micrograms/kg · SC or PO · two to three times a day · As fourth line therapy after prostaglandin synthetase inhibitors, opioid agonists, and 5-HT3 serotonergic antagonists are being used.
- Epidural analgesia/analgesia · 2-3 micrograms/kg diluted to 8 mL with sterile normal saline · epidurally · Single dose · Onset/duration of analgesia = 19 minutes/192 minutes with 2 mcg/kg dose and = 9 minutes/311 minutes with 3 mcg/kg dose; peak effects from 60-180 minutes.
- Diagnosing hyposomatotropism · 10 micrograms/kg · IV · Single dose · Obtain plasma for GH levels prior to dosing and at 15, 30, 45, 60, and 120 minutes. Healthy dogs should demonstrate GH levels of 10 ng/mL after administration.
- Adjunctive antidiarrheal therapy for refractory cases of inflammatory bowel disease · 5-10 micrograms/kg · PO or SC · two to three times a day · Can activate alpha2-receptors in the CRT and cause vomiting.
- Control panic-like responses and fear-based behavioural problems · Dose not specified in monograph; use tactically (prn) or over longer term · PO · prn or daily · prn (lasts 3-4 hours) or long-term (takes 1-2 weeks for full response) · Effect develops in about 30 minutes. Withdrawal must be gradual.
- Diagnostic test for pituitary dwarfism (hyposomatotropism) · Dose not specified in monograph · IV · Single dose · N/A · Specialist texts should be consulted for the clonidine stimulation test protocol.
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給藥途徑
禁忌症
- Known hypersensitivity to clonidine
- Severe cardiovascular disease (use with extreme caution)
- Renal disease (use with extreme caution)
不良反應
- Transient hyperglycemia
- Dry mouth
- Constipation
- Sedation
- Aggressive behavior
- Hypotension
- Collapse
- Bradycardia
- Transient sedation
- Rebound hypertension (if withdrawn abruptly)
藥物相互作用
- Antihypertensive drugs · Possible additive hypotensive effects
- Beta-adrenergic blocking agents (e.g., propranolol) · May enhance bradycardia. If discontinuing, beta-blocker should be stopped first, then clonidine tapered to avoid rebound hypertension.
- CNS depressant drugs (opiates, barbiturates) · May exacerbate the actions of other CNS depressant drugs
- Digoxin · Possible additive bradycardia
- Prazosin · May decrease the antihypertensive effects of clonidine
- Tricyclic antidepressants (e.g., amitriptyline) · May block the antihypertensive effects of clonidine
- Barbiturates · Increased central nervous system depression and hypotension · major
- Opiates · Additive sedation, bradycardia, and respiratory depression · major
- Beta-blockers · Additive hypotensive and bradycardic effects; may exacerbate rebound hypertension upon withdrawal · major
- Hypotensive agents · Additive lowering of blood pressure · moderate
監測
- Growth Hormone (GH) levels and adverse effects (when used for diagnostics)
- Blood pressure
- Heart rate
- Efficacy and adverse effect profile (when used for ongoing diarrhea treatment)
- Degree of sedation
- Behavioral response
- Plasma IGF-1 or GH levels (when used diagnostically)
過量
Clonidine has a **narrow margin of safety**. * **Clinical Signs:** Hypotension, bradycardia, vomiting, weakness, depression, lethargy, tachycardia, ataxia, and hypertension. Rarely, seizures or respiratory depression. * **Toxicity Values:** LD50 for oral clonidine in rats is 465 mg/kg; mice 206 mg/kg. * **Treatment:** For large overdoses, gut evacuation using standard protocols (use emetics cautiously as consciousness may deteriorate rapidly). Symptomatic and supportive care. Fluids and pressors (e.g., dopamine) for hypotension. IV atropine for bradycardia. **Atipamezole or yohimbine** may be used to reverse cardiovascular effects, but multiple doses may be required as signs can last up to 48 hours.
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